Peptide-based drugs are highly effective medicines with relatively short duration of action and variable therapeutic index. The present disclosure is directed to peptide-based prodrugs wherein the prodrug derivative is designed to delay onset of action and extend the half life of the drug. The delayed onset of action is advantageous in that it allows systemic distribution of the prodrug prior to its activation. Accordingly, the administration of prodrugs eliminates complications caused by peak activities upon administration and increases the therapeutic index of the parent drug.
Receptor recognition and subsequent processing of peptide and protein agonists is the primary route of degradation of many peptide and protein-based drugs. Thus binding of the peptide drug to its receptor will result in biological stimulation, but will also initiate the subsequent deactivation of the peptide/protein induced pharmacology through the enzymatic degradation of the peptide or protein. In accordance with the present disclosure, prodrugs can be prepared to extend the peptide or protein's biological half life based on a strategy of inhibiting recognition of the prodrug by the corresponding receptor.
The prodrugs disclosed herein will ultimately be chemically converted to structures that can be recognized by the receptor, wherein the speed of this chemical conversion will determine the time of onset and duration of in vivo biological action. The molecular design disclosed in this application relies upon an intramolecular chemical reaction that is not dependent upon additional chemical additives, or enzymes.
Pre-proglucagon is a 158 amino acid precursor polypeptide that is processed in different tissues to form a number of different proglucagon-derived peptides, including glucagon (SEQ ID NO: 701), glucagon-like peptide-1 (GLP-1; amino acids 7-36 are provided as SEQ ID NO: 703 and SEQ ID NO: 704), glucagon-like peptide-2 (GLP-2; SEQ ID NO: 708) and oxyntomodulin (OXM; SEQ ID NO: 706), that are involved in a wide variety of physiological functions, including glucose homeostasis, insulin secretion, gastric emptying, and intestinal growth, as well as the regulation of food intake.
Glucagon is a 29-amino acid peptide (that corresponds to amino acids 33 through 61 of pre-proglucagon, while GLP-1 is produced as a 37-amino acid peptide that corresponds to amino acids 72 through 108 of pre-proglucagon. GLP-1(7-36) amide (SEQ ID NO: 704; the C terminus is an arginine amide) or GLP-1(7-37) acid (SEQ ID NO: 703; C terminus is a glycine) are biologically potent forms of GLP-1, that demonstrate essentially equivalent activity at the GLP-1 receptor.
Glucagon is a life-saving medicine that is used in the acute treatment of severe hypoglycemia. Oxyntomodulin has been reported to have pharmacological ability to suppress appetite and lower body weight. Clinical studies with GLP-1 receptor agonists or stabilized GLP-1 analogs have proven this family of peptides to be an effective treatment for Type II diabetes. In addition, it might be intrinsically safer than insulin therapy because of its glucose dependent action, thus eliminating the chances of hypoglycemia. Structure-activity relationship studies have shown that the N terminal histidine for each of these three peptides (glucagon, GLP-1 and oxyntomodulin) is especially important for the full action and that N-terminally extended forms severely diminish biological potency.
Additional peptides are known that resemble glucagon and GLP-1 in structure and have similar activities. For example, Exendin-4 is a peptide present in the saliva of the Gila monster that resembles GLP-1 in structure, and like glucagon and GLP-1, increases insulin release.
In addition, gastric inhibitory polypeptide (GIP) is also known as a glucose-dependent insulinotropic peptide, and is a member of the secretin family of hormones. GIP is derived from a 153-amino acid proprotein encoded by the GIP gene and circulates as a biologically active 42-amino acid peptide (SEQ ID NO: 707). The GIP gene is expressed in the small intestine as well as the salivary glands and is a weak inhibitor of gastric acid secretion. In addition to its inhibitory effects in the stomach, in the presence of glucose, GIP enhances insulin release by pancreatic beta islet cells when administered in physiological doses. GIP is believed to function as an enteric factor that stimulates the release of pancreatic insulin and that may play a physiological role in maintaining glucose homeostasis.
Osteocalcin (SEQ ID NO: 709) is a noncollagenous protein found in bone and dentin. It is secreted by osteoblasts and thought to play a role in mineralization and calcium ion homeostasis. Osteocalcin has also been reported to function as a hormone in the body, causing beta cells in the pancreas to release more insulin, and at the same time directing fat cells to release the hormone adiponectin, which increases sensitivity to insulin.
One disadvantage associated with the therapeutic use of bioactive peptides such as osteocalcin, GIP, glucagon, GLP-1 and oxyntomodulin is their extremely short half-life (approximately two minutes for glucagon and GLP-1) in plasma. Accordingly, to obtain reasonable glycemic control, native glucagon-related peptides would need to be administered continuously for a prolonged period of time. The short half life of glucagon and GLP-1 related peptides results from the rapid degradation by Dipeptidyl Peptidase IV (DPP-IV), which cleaves between the second and third amino acids. This cleavage not only inactivates the native peptides but in the case of glucagon and GLP-1 the shortened forms could be functional antagonists at their respective receptors. Accordingly, there is a need for longer-acting variants of GIP, glucagon, GLP-1, and oxyntomodulin, and related peptides, to realize the full therapeutic potential of these mechanisms of drug action